The present invention relates to a monoclonal antibody against a specific human apolipoprotein A-I (hereinafter referred to as xe2x80x9capoA-Ixe2x80x9d); a method of immunologically assaying a specific apoA-I by use of the antibody; and an immunological assay reagent containing the antibody.
ApoA-I is a predominant apoprotein that constitutes HDL and plays an important role in reserve cholesterol transportation from peripheral cells to the liver (Philips M. C. et al., Biochem. Biophys. Acta, 906: p. 223 (1987)). Therefore, apoA-I assay is performed in the diagnosis of arteriosclerosis.
In recent years, researchers have elucidated that an HDL containing apoA-I but containing no apolipoprotein A-II (hereinafter referred to as xe2x80x9capoA-IIxe2x80x9d) (Ishizuka et al., xe2x80x9cIgaku to Yakugaku,xe2x80x9d Vol. 39, No. 5, p. 1041, 1988) exhibits a stronger effect of pulling cholesterol from cells as compared with an HDL containing both apoA-I and apoA-II, and that an apoA-I not binding to a lipid and an apoA-I which is in the form of small particles and occurs in prexcex21-HDL containing a small amount of lipid (T. Miida et al., Biochemistry, 29: p. 10469 (1990)) play an important role in reverse cholesterol transport system from cells. Accordingly, assaying these specific apoA-I""s is of increased importance. Among HDLs containing apoA-I but containing no apoA-II, prexcex21-HDL pulls cholesterol from peripheral cells through interaction specific to the cell surface (Fielding, C. et al., Lipid Res., 36: p. 211-228 (1995)), and its action is more effective than that of HDL. Thus, prexcex21-HDL is particularly attracting researcher"" attention.
However, since no antibody that selectively reacts with a specific apoA-I has been found, the target apoA-I must be isolated from other apoA-I""s through a method such as electrophoresis or immune precipitation. Thus, a specific apoA-I cannot be assayed in a simple manner.
In view of the foregoing, the present inventors have carried out extensive studies and have successfully obtained a monoclonal antibody which specifically reacts with a certain species of apoA-I. The inventors have found that, by use of the monoclonal antibody, apoA-I""s such as the aforementioned apoA-I not binding to a lipid and apoA-I composing prexcex21-HDL can be assayed accurately in a simple manner, thereby enabling more accurate diagnosis of lipid metabolism disorder to be performed. The present invention has been accomplished on the basis of this finding.
Accordingly, the present invention provides a monoclonal antibody reacting specifically with (1) an apoA-I occurring in HDL which contains no apoA-II and has a molecular weight of 150,000 or less and (2) an apoA-I not binding to a lipid.
The present invention also provides a hybridoma for producing the monoclonal antibody.
The present invention also provides a method of immunologically assaying apoA-I, characterized by reacting the monoclonal antibody with a specimen.
Furthermore, the present invention provides a reagent for assaying an apoA-I containing the monoclonal antibody.